Factors affecting IP addresses to be returned

Information considered when determining IP addresses to return

A GRM server evaluates many factors when determining how to redirect a client request. The following illustration shows what the GRM server considers to determine the IP addresses to return when it receives a DNS query (if the server is a GRM DNS server) or a client request (if the server is a GRM L7 server).

Details about the preceding flow chart are discussed in the following paragraphs.

Is the request or query from an edge group?

The GRM server first checks the list of CIDR blocks in its configuration to determine whether the client request or DNS query is associated with an edge group.

If the GRM server can make a match, it next considers any policies that have been set and other factors that affect eligibility.
If the GRM server cannot make a match, it tries to find previous proximity information to enable it to determine the GRM agent caches close to the client.

Discarding caches not meeting policies and other criteria

Before a GRM server returns GRM agent cache IP addresses to a client, it eliminates any GRM agent caches that do not meet policies or other controls that have been set. The GRM server evaluates a number of factors to determine whether a cache meets the criteria to be returned to a client, as follows:

The GRM server applies optional controls that have been set, for example, the threshold for the CPU activity of a center or edge cache and availability. For more information, see Status information provided to the GRM server.
The GRM server applies any GRM domain filtering criteria that might have been specified for the domain, and it returns IP addresses of eligible center and edge caches to the client.
If the GRM server is not directing content requests for the host or domain, then
- A GRM DNS server passes the DNS query to the authoritative DNS nameserver for which it is the front end.
- A GRM L7 server serves the client content request itself;.
See GRM domains and their use for IP address filtering for details about domains.

Note
A GRM DNS server returns the IP addresses of all eligible edge and center caches. If a proxy.pac file is used to direct client requests to a GRM L7 server, the GRM L7 server might return the IP address of more than one GRM agent cache close to the client. If another method is used, the GRM L7 server rewrites the client request with the IP address of only one GRM agent cache.

If the request is not from an edge group and no proximity measurement exists

The process a GRM server follows differs, depending on whether it is a GRM DNS server or GRM L7 server.

GRM DNS server
If the GRM DNS server cannot measure proximity, or if it has not determined proximity to a local DNS nameserver previously, the GRM server uses the IANA database to narrow down the list of eligible caches to be returned by matching the client's IP address to a continent.

The GRM server does not have proximity information in its database in the following circumstances:
- The local DNS nameserver has not previously queried the GRM server, so no proximity measurements were made.
- Caches reported that a local DNS nameserver was inaccessible, so the GRM server discarded the proximity data for it.
- A local DNS nameserver has not contacted the GRM server recently (within a maximum of 30 days), so the GRM server discarded the DNS entries for the local DNS nameserver.
GRM L7 server
When the GRM L7 server receives the first request from a new client, it has no proximity information about that client.
- If the Force Redirection option is enabled (the default), the GRM L7 server will force redirection of that request to the most appropriate agent, based on the responses the server receives from its agents to its request for proximity measurements. If the GRM L7 server does not receive a response for redirection information from its GRM agent caches within 30 seconds, the GRM L7 server serves the content itself.
- If the Force Redirection option is disabled, the GRM L7 server automatically serves the content itself. During the process, the GRM L7 server collects the proximity information that it can use the next time it receives a request from the client.
The GRM L7 server serves content to a client directly in the following additional circumstances:
- No edge cache or center cache that meets the domain filtering criteria is available.
- The GRM L7 server receives a request for a type of HTTP content that is not listed in the HTTP Redirection Suffix option.